Cold producing systems



June 3, 1969 J. A. RIETDIJK I 3,447,339

. COLD PRODUCING SYSTEMS Filed May 12, 1967 Sheet INVENTOR.

JOHAN A. RIETDUK BY w AGEN June 3, 1969 J. A. RIETDIJK 3,447,339

COLD PRODUCING SYSTEMS Filed, lay 1 2. 1967 Sheet 2 of a INVENTORV JOHAN A. RIETD'JK BY ZZMJ; ,6

AGEN

June 1969 .1. A. RIETDIJK 3,447,339

COLD PRODUCING SYSTEMS Filed lay 12, 196? Sheet 5 or :s

INVENT OR.

JOHAN A. RIET D'JK BY GEN United States Patent 0 U.S. Cl. 62-500 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a cold producing apparatus for cooling an electronic element including its current conductors which extend to a higher temperature environment and produce heat during operation of the element. The apparatus includes means for compressing a fluid medium, a heat exchanger for initial cooling of the medium to a temperature below its inversion temperature, an ejector for expanding and cooling the medium to a lower intermediate temperature and pressure, and a first reservoir for receiving said expanded medium and conducting it through a choke to a second reservoir at a lower temperature and pressure.

The invention relates to a cold producing system for cooling devices such as cryogenic storage elements or memories, calculating elements of electronic computers, and coils, which operate at very low temperatures. Cooling of these devices during their operation is required because of the heat produced internally and heat resulting from their contact with current connectors or other heat conducting connections.

In known cold producing systems the elements operating at a very low temperature are arranged in a bath containing a liquid such as helium, boiling at a low temperature. The desired operational temperature of these elements is usually on the order of 3 K. and less, and these temperatures are related to vapour pressures of helium of about 0.25 ata. and less. Owing to the current flow through conductors and the other heat-conducting connections, a quantity of heat will pass from the environments of higher temperature to the elements operating at the lower temperature. Due to this penetrating heat and the developed heat respectively, a quantity of helium will be evaporated in the bath. In order to compensate for the losses of liquid helium, use may be made of a Joule-Kelvin system, in which the helium is compressed, cooled and expanded, so that during the expansion part of the helium becomes liquid. When such a system is employed, the compressor must have a suction pressure of 0.25 ata. or less for maintaining the desired pressures above the liquid of 0.25 ata. and less. It will be obvious that this involves a very bulky compression system with a very high compression ratio. In such a system the low-pressure side of the heat exchangers must have a low flow resistance, which requires complicated, large and hence expensive heat exchangers. A further disadvantage of such a system is that the expansion takes place at least partly in Joule-Kelvin cocks, in which the pressure energy of the high-pressure medium is dissipated, which means a loss.

The invention has for its object to obviate the aforesaid disadvantages and is characterized in that the cold producing member comprises a compression member for compressing a medium, the outlet of compressed medium communicating with one or more heat exchangers in which the compressed medium is cooled to below the inversion temperature associated with the medium pressure. The system further comprises at least one ejector to which the cooled high-pressure medium can be supplied. The outlet of each ejector communicates lower pressure medium to a first reservoir which communicates via one outlet through a heat exchanger to the suction side of the compression member. This first reservoir also communicates via a second outlet through a choking member to a second reservoir in which lower pressures prevail than in the outlet or the first reservoir, and the additional reservoir communicates through a heat exchanger with the suction side of an ejector. The said cooled elements operating at a very low temperature are disposed in thermal contact or with at least the second reservoir in which the lowest pressure prevails, while the current conductors or the other heat-conducting connections are in thermal contact with the outlet of the ejector, the first reservoir, if used, or the medium contained therein, and with the further reservoir in which the lowest pressure prevails.

In the scope of the present invention an ejector is to denote a device in which the potential energy of a highpressure (primary) medium is converted wholly or partly into kinetic energy, which is used at least partly for raising the pressure of a second (secondary) medium.

In the system according to the invention the energy of the high-pressure medium supplied to each of the ejectors is utilized at least partly for drawing off the vapour from the 'further low-pressure reservoir or reservoirs, and to compress this vapour to the pressure prevailing in the ejectors outlet or the pressure in the first reservoir communicating with the suction side of the compressor. In this system the suction pressure of the compressor is therefore no longer equal to the pressure prevailing in the second reservoir in which are arranged the elements operating at a very low temperature, but it is equal to the higher pressure prevailing in the outlet of the ejector. This has the great advantage that the compression device of this system may be smaller, and that the compression ratio may be lower. This is achieved without the addition of a device compressing the vapour of the lower-pressure eservoir to the pressure of the reservoir communicating with the suction side of the compressor and without consuming additional energy. The great difference from the known system is that instead of a choking cock, use is made of an ejector in which the pressure energy of the high-pressure medium is not dissipated uselessly, but is utilized for compressing the vapour of the lower-pressure reservoir to the suction pressure of the compressor. The resultant system has higher efliciency and a more favourable pressure ratio in the heat exchanger and across the compressor, so that the system is cheaper and has a smaller volume.

In the cold system according to the invention the elements operating at the low temperature are connected via current conductors and other heat-conducting connections to environments of higher temperature, and these connections a given flow of heat will be conducted towards the elements. In order to avoid a rise in temperature, this penetrating heat has to be compensated, which is achieved by the evaporation of part of the condensate of the reservoir and by the removal of this vapour from the reservoir. If the current conductors and the further heatconducting connections were in direct contact with the elements operating at low temperature, the whole ilow of penetrating heat would be received in the reservoir in which the elements are arranged and in which the lowest temperature prevails. This produces a development of vapour in this reservoir. In order to maintain the desired temperature and pressure in this reservoir the vapour has to be drawn off by the ejector.

The ejector is capable of converting the expansion power of the primary medium with a given efficiency into compressive power for the secondary medium, with efficiencies of conventional ejectors being about 25%. If in a given case a predetermined primary flow of a mass with a given temperature is available, and if it is desired to maintain a given pressure in the reservoir to be emptied at the in-flow of a given quantity of heat, a given pressure will be produced in the first reservoir which communicates with the outlet side of the ejector.

If, in accordance with the invention, the current conductors and other heat-conducting connections are first brought into thermal contact with the outlet of the ejector or the first reservoir, a great portion of the penetrating heat will be captured at this place. Consequently, less vapour will be developed in the reservoir to be emptied, which means that the efficiency of the ejector may be lower. If the etficiency of the ejector remains the same, the pressure in the first reservoir may be higher. This means that the suction pressure of the compressor will be higher, so that the compression ratio is lower and the efiiciency of the system is higher.

The invention will be described more fully with reference to the drawing.

FIGURES 1, 2 and 3 show diagrammatically, not to scale, three embodiments of cold producing systems.

Referring to FIGURE 1, reference numeral 1 designates a compressor. The compressed medium is first passed through a cooler 2, in which the compressive heat is conducted away. The compressed medium then flows through a heat exchanger 3, where it exchanges heat with a lowerpressure medium. The high-pressure medium is subsequently cooled in a heat exchanger 4 by means of a cooler 5 to a temperature of, for example, 60 K. The high-pressure medium then flows through a heat exchanger 6, where it exchanges heat with a lower-pressure medium. The high-pressure medium is cooled in a heat exchanger 7 with the raid of the cooler 8 to a temperature of, for example, K., and in the heat exchanger 9 it exchanges heat with expanded medium. The temperature of the high-pressure medium is then below the inversion temperature of the medium at the prevailing pressure. The medium then enters an ejector 10, in which its pressure is reduced. The ejector communicates with an outlet 11, and to a reservoir 12. The vapour space of the reservoir 12 communicates via the heat exchangers 9, 6 and 3 with the inlet side of the compressor 1. The condensate of the reservoir 12 can flow via the heat exchanger 13- and the choking cock 14 in which the pressure of the liquid is further reduced, to the reservoir 15 in which a lower pressure prevails than in the reservoir 12. The vapour space of the reservoir 15 communicates through the heat exchanger 13 with the suction side 16 of the ejector 10. The reservoir 15 accommodate a cryogenic memory element 17 of an electronic computer, connected through current conductors (two of them 18 and 19 are shown) to an environment of higher temperature.

The medium in this system is helium, and for satisfactory operation of the memory 17, it is desirable to maintain its temperature at about 3 K., which is associated with a vapour pressure of helim of about 0.25 ata.

The current conductors 18 and 19 are connected at one end to an environment of ambient temperature and at the other end to the memory 17 at 3 K. Owing to the difference in temperature heat will leak into the memory. When current passes, Joules heat will be developed in the current conductors. Above the plane II the current conductors are in thermal contact with the medium in the heat exchangers 3, 4, 6, 7 and 9. After the last cooler the current conductors could enter the memory 17 without exchange of heat. This means that along the last portion of the current conductors a temperature gradient from 15 K. to 3 K. would prevail, so that a given quantity of heat might leak away towards the reservoir 15. This quantity of heat is compensated by the evaporation of a 4 given quantity of helium in the reservoir 15. In order to maintain a pressure of about 0.25 ata. in this reservoir, the developed vapour has to be removed from the reservoir 15, which is achieved by the ejector 10, the suction side of which communicates with the reservoir 15. With a given efiiciency the ejector converts the potential energy of the high-pressure medium into energy employed for drawing off vapour from the reservoir 15 and for com pressing it to the pressure prevailing in the reservoir 15. With a given efliciency of the ejector and a given primary flow of medium, the pressure in the reservoir 12 will be lower according as a larger quantity of vapour has to be withdrawn from the reservoir 15. A low pressure in the reservoir 12 is harmful for the system, since the heat exchangers are then constructurally more complicated and the compressor must have greater dimensions and a higher compression ratio.

In order to obviate all these disadvantages, the current conductors 18 and 19 of the cold producing system of FIGURE 1 are also in thermal contact with the helium in the reservoir 12 and/ or with the heat exchanger. This has the advantage that a great portion of the heat leaking away towards the lowest temperature is absorbed already at the temperature of the reservoir 12, so that the quantity of vapour to be withdrawn from the reservoir 15 is smaller, which results in a higher pressure in the reservoir 12. This involves the advantage that the compressor and the compression ratio may be smaller, which provides a structural simplification and an economy of power.

Although the system shown in FIGURE 1 comprises a reservoir 12 at the outlet 11 of the ejector, this reservoir may be dispensed with, so that at this place the outlet 11 directly splits up into a duct towards the heat exchanger 9 and a duct to the heat exchanger 13. The current conductors can then be in direct thermal contact with the outlet 11. The compressor may, of course, be of ,any conventional type independently of the compression ratio in one or more stages.

The coolers 8 and 9 may be formed by the freezers of a two-stage Stirling cold-gas refrigerator, or other coolers may be employed. It is possible, for example, to use as coolers expansion turbines, in which a portion of the high-pressure medium is expanded to the suction pressure of the compressor. In this case the compressor serves as a driver for the coolers 8 and 9 and the ejector, in which the advantage of the higher suction pressure obtainable by an ejector system, and particularly by the system of the present invention, is of very great advantage.

Although the system of FIGURE 1 comprises only one ejector, the invention may, of course, be applied to cold producing systems comprising a plurality of ejectors.

FIGURE 2 shows diagrammatically a cold producing system comprising two series-connected ejectors 20 and 21, and a heat exchanger 20a disposed between the ejectors. The reservoir 12 communicates through a heat eX- changer 22 and a choking cock 23 with a further reservoir 24, which communicates through the heat exchanger 13 and the choking cock 14 with the reservoir 15, in which the memory 17 is disposed. The vapour spaces of the reservoirs 24 and 15 communicate with the suction sides of the ejectors 21 and 20 respectively. The current conductors 18 and 19 are in thermal contact with the reservoirs 12, 24, and 15, which provides the above-described advantages. The operation of this system will be obvious, as it corresponds to that of FIG. 1.

FIGURE 3 shows diagrammatically a cold producing system comprising two parallel-connected ejectors 30 and 31. These ejectors both communicate with the highpressure side of the heat-exchanger 9, and with heat exchanger 9a. The outlet 11 of the ejector 30 communicates with the reservoir 12, and the outlet 32 of the ejector 3-1 communicates with a further reservoir 33. Through the heat exchanger 34 and the choking cock 35 the reservoir 12 communicates with the reservoir 33, the latter communicating through the heat exchanger 13 and the choking cock 14 with the reservoir 15 accomodating the memory 17. The current conductors 18 and 19 are in thermal contact with the medium in the reservoirs 12 and 33 so that the major portion of the heat flowing in the direction of the memory 17 is absorbed at higher temperature levels.

From the foregoing it will be obvious that the invention provides a cold producing system including one or more ejectors, wherein heat is transferred with a high degree of efiiciency from an environment at very low temperature to a place of higher temperature.

What is claimed is:

1. In a cold producing apparatus for maintaining at least one electronic element therein at a relatively low temperature, said element being provided with current conductors which produce heat and are connected to locations at higher temperatures; the improvement comprising a means for compressing a medium, a plurality of heat exchangers in which the compressed medium is cooled to below the inversion temperature associated with the pressure of said medium, at least one ejector to which said cooled high pressure medium is supplied, a reservoir having the lowest pressure of the apparatus, a choking member, the outlet of said ejector having two branches, the first communicating fluid through said choking member to said reservoir, said reservoir communicating with the suction side of said ejector, the second branch communicating fluid through said heat exchangers to the suction side of the compressor, said electronic element operating at a low temperature being in thermal contact with said reservoir, and the current conductors of said element being in thermal contact with at least the outlet of said ejector and said reservoir.

2. A cold producing apparatus for cooling an electronic element to a relatively low temperature, the element being connected to current conductors which extend to a higher temperature environment and produce heat during operation of the element comprising:

(a) means for compressing a fluid medium,

(b) a first heat exchanger for receiving and cooling the compressed medium to a first temperature below its inversion temperature and above the critical temperature associated with the pressure thereof,

(c) at least one ejector having (1) a first inlet for receiving from the heat exchanger cooled medium in a gaseous state, which medium is expandable in the ejector to a second intermediate temperature and pressure below that in the heat exchanger, (2) an outlet through which expanded medium is dischargeable, and (3) a suction inlet for pumping medium therein,

(d) a first reservoir having an inlet for receiving said expanded medium from the ejectors outlet, and first and second outlets,

(e) a choke means through which medium (from the first containers first outlet) is further expandable to a third pressure below that of the second pressure, and

(f) a second reservoir having an inlet for receiving the further expanded medium and an outlet to which medium in vapor state is pumped to the suction inlet of the ejector,

(g) first means for thermal contact between medium in said second reservoir and the electronic element for cooling the element, and

(h) second means for thermal contact between said current conductors and medium in said first and second reservoirs respectively.

3. Apparatus as defined in claim 2 further comprising a second heat exchanger wherein medium flowing between the first reservoir and choke means is cooled by medium flowing between the second reservoir and the suction inlet of the ejector.

4. Apparatus as defined in claim 2 further comprising (a) a second choke, (b) a second ejector similar to and disposed in series with said first ejector between said first ejector and said first heat exchanger, (c) a third reservoir having an outlet connected to the suction inlet of the second ejector and an inlet, said second reservoir having a second outlet connected through said second choke to the inlet of said third reservoir, and (d) third means for thermal contact between said current conductors and medium in said third reservoir.

5. Apparatus as defined in claim 2 further comprising: (a) a second ejector similar to and disposed in parallel with the first ejector, (b) a third reservoir and an associated choke disposed in series between said first heat exchanger and first reservoir, the third reservoir having an inlet connected to the outlet of said second ejector and an outlet connected to said first reservoir, the first reservoir having an additional outlet connected to the suction inlet of said second ejector, and ((1) third means for thermal contact between said current conductors and medium in said third reservoir.

6. A cold producing apparatus for maintaining an electronic element at a relatively low temperature, the element being connected to current conductors which produce heat and extend to a higher temperature environment; the improvement comprising:

(a) means for compressing a fluid medium;

(b) a first heat exchanger for receiving a compressed medium and cooling it to below the inversion temperature associated with the pressure thereof;

(0) at least one ejector to which said cooled high pressure medium is supplied;

(d) a first reservoir having (1) an inlet for receiving low pressure medium from said ejector, (2) a first outlet communicating with said compressing means, and (3) a second outlet;

(e) a choke means for expanding medium from said first reservoirs second outlet to a lower pressure and temperature;

(f) a second reservoir having an inlet for receiving expanded medium from said choke means, and an outlet for communicating vapor therein to the suction outlet of an ejector;

g) a second heat exchanger for cooling medium flowing to the choke with medium discharged from the second reservoir; and

(h) said electronic element being in thermal contact with said second reservoir for operating at a low temperature, and the current conductors of the element being in thermal contact with at least said first and second reservoirs respectively.

References Cited UNITED STATES PATENTS 3,349,161 10/1967 Latham 62-5l4 3,360,955 1/1968 Witter 625l4 3,371,145 2/ 1968 Camille 62514 WILLIAM J. WYE, Primary Examiner.

US. Cl. X.R. 62-514 

